1. Technical Field
This invention relates to an aqueous coating composition such as a floor finish that contains a plasticizing agent that comprises at least one tertiary alkyl monocarboxylic acid.
2. Background Art
Aqueous coating compositions are well known and find use as protective coatings for various substrates such as wood, metal, plastic and the like. Such compositions typically contain a film-forming polymer such as an acrylic polymer. That polymer forms a continuous protective coating over the substrate to, often in conjunction with other additive materials such as other polymers, pigments, dyes, ultraviolet light absorbing agents and the like, help protect it from damage caused by the sun, abrasion, foot traffic, pressure, and so forth. The film-forming polymers are typically selected for their physical properties such as water solubility, flexibility, hardness, resilience, toughness and the like to fit the needs of the substrate being protected and the environment in which the coating will be used.
One way to modify the properties of the polymers included in the coating composition is to include a "plasticizing agent" or "plasticizer". A plasticizing agent is typically a compound that can associate with the polymer and thereby modify the physical properties of the polymer or of the coating composition itself. For example, a plasticizing agent may serve to change the hardness, flexibility, or ability of a polymer or a coating formed from it to form a continuous film. The plasticizing agent is thus used to impart desirable properties to the film left behind when the coating composition is applied to the substrate and the volatile components are removed such as by drying. These desirable results are achieved by the plasticizing agent without having to change the nature of the polymer itself or to obtain properties that are not possible to get by simply modifying the polymer itself.
Plasticizers are commonly added to aqueous floor finishes as can be seen from an examination of U.S. Pat. No. 3,467,610 to Fiarman et al.; U.S. Pat. No. 3,320,196 to Rogers; U.S. Pat. No. 3,308,078 to Rogers et al.; U.S. Pat. No. 4,013,607 to Dwyer et al.; and U.S. Pat. No. 4,317,755 to Gregory. The plasticizing agents employed may be of the permanent type that are insufficiently volatile to remain in the coating film after drying or of the fugitive type that substantially evaporate along with the water and other volatile components of the coating composition during the drying process. One of the most commonly used plasticizing agents is tributoxyethyl phosphate since it not only acts as a plasticizer, but also facilitates good coating film formation as a leveling agent as noted in the Gregory '755 Patent. Tributoxyethyl phosphate is a somewhat expensive raw material and its use adds a significant cost to the composition.
One attempt to avoid the use of a plasticizer such as tributoxyethyl phosphate in a floor finish composition is U.S. Pat. No. 4,460,734 to Owens et al. that teaches self leveling aqueous floor polish compositions that do not require the use of tributoxyethyl phosphate as a leveling agent. Instead, Owens et al. teach using polyalkoxylated linear aliphatic alcohols as leveling agents.
Fatty acids and salts are also taught as being useful in aqueous floor finish compositions, but the purpose for their use is in the form of fatty acid salts to serve as emulsifiers or leveling agents as noted in the Rogers '196, Rogers et al. '078 and Gregory '755 Patents. The Gregory '755 Patent notes that the fatty acids useful include C.sub.12 -C.sub.18 fatty acids of animal, vegetable or synthetic origin and prefers the use of tall oil fatty acids in amounts of up to 10% when such ingredients are used.
As will be discussed later, I have found that a certain class of synthetic fatty acids, C.sub.6 -C.sub.30 tertiary alkyl monocarboxylic acids, unexpectedly provide very beneficial properties to aqueous coating compositions when they are used as a portion of the total amount of plasticizing agent in such compositions, especially in aqueous floor finish compositions.
The C.sub.6 -C.sub.30 tertiary alkyl monocarboxylic acids have been known for some time and some of them are commercially available from Exxon Chemical Americas of Houston, Tex. under the trade name of "NeoAcids" such as "Neo Decanoic Acid" that has an average of 10 carbon atoms per molecule. Except for certain purified products, these products are typically provided as mixtures of structural isomers. Their properties and potential uses are described in Exxon's product brochure no. SC89-134-500C entitled NeoAcids Properties, Chemistry and Applications, copyright 1982 (16 pages). However, the use of such acids in unmodified form as plasticizing agents is not suggested in that brochure. A tertiary alkyl monocarboxylic acid having an average of 10 carbon atoms per molecule is also commercially available as "Versatic Acid" from Shell Chemical Company of Houston, Tex.
U.S. Pat. No. 3,037,955 to Carman teaches thermoplastic acrylic resin coating compositions that are organic solvent solutions of such resins. These compositions may include from 0.5% to 3.0% of an acid or anhydride in the composition to improve the adhesion of the coating to a substrate when it is dried at up to 180.degree. F. (82.2.degree. C.). Among the various acids and anhydrides that are said to be useful is ethyl hexoic acid that is a C.sub.8 secondary alkyl monocarboxylic acid rather than a tertiary alkyl monocarboxylic acid. These coating compositions are not aqueous compositions.
Two Patents to Inskip, U.S. Pat. Nos. 4,180,620 and 4,210,705, describe the use of from 0.01% to 0.5% by weight of a divalent metal salt of neo decanoic acid as an adhesion control agent for polyvinyl butyral. Nothing is said concerning the use of the monocarboxylic acids alone as a plasticizing agent. Inskip teaches that quantities in excess of 0.5% provide little or no additional benefit.
U.S. Pat. No. 4,274,973 to Stanton teaches the use of tertiary alkyl monocarboxylic acids such as neodecanoic acid in aqueous water-soluble soap lubricants for conveyor belts and the like to reduce viscosity of the lubricants and to improve lubricity effectiveness. The Stanton compositions do not contain film-forming polymers and are aqueous mixtures of 2%-40% by weight of fatty acid soaps and neodecanoic acid that may optionally further include anionic or cationic surfactants, and chelating agents.